Take a look at whether your client qualifies for foreign earned income exclusion under physical presence test or bona fide resident test.  Pubs from the IRS are easy to understand but you will find the technical details under §911 and its regulations.

If the foreign earned income cannot be fully excluded, foreign tax credit may be claimed to alleviate double taxation.

Besides basic compensation reporting, there is a whole host of international tax issues and US reporting obligations that need to be considered, mitigated, and/or fulfilled.  Many a time, there are serious consequences for failure to comply.  In case you are not familiar with structures of foreign compensation and benefit plans, which do not conform to US regulations, as well as various US international tax provisions, you should be ready to invest a substantial amount of time to research all the related topics or consider farming this out to someone who specializes in expatriate and international tax.